This invention relates to a multi-layered twisted nematic liquid crystal display panel wherein a plurality of layers of liquid crystal cells are disposed each having a so-called twisted nematic liquid crystal composition between a pair of plates with its spiral axis normal to the plates and its longitudinal axes of the liquid crystal molecules twisted approximately 90.degree. in relation to the plates.
As is well known in the art, a twisted nematic liquid crystal display manifests a strong anisotropy and hence a viewing angle dependency in display contrast when being supplied with an effective voltage of an amplitude less than a three-fold value of the threshold level of its optical effects (cf. "Some Characteristics in Twisted Nematic Field Effect Liquid Crystal Displays" by Funada, Uede, Wada and Mito, Applied Physics, 44, 866, 1975). The viewing angle dependency is governed by the twisting direction (chirality) of liquid crystal molecules and the tilting direction (tilt angle) of the liquid crystal molecules with respect to a surface of a substrate. The liquid crystal molecules, therefore, bear the same chirality and tilt angle within a common liquid crystal cell, bringing a highest contrast area into agreement with the viewer's direction of observing the liquid crystal cell. This is of a significant importance in minufacturing twisted nematic liquid crystal cells with high quality of display (cf. Japanese unexamined patent publication No. 51/4996). As disclosed in Japanese unexamined patent publication No. 50/794, a multi-layered twisted nematic liquid crystal display panel has been proposed in which such twisted nematic liquid crystal cells are built in a multi-layer fashion and an electrode structure is made to apply partially an electric field to respective ones of liquid crystal layers in the cells as well as a built-in drive circuit for applying desired voltage levels to respective electrodes in the cells. This multilayered twisted nematic liquid crystal display panel is advantageous over a single layer panel as follows:
(1) Diverse displays are possible;
(2) Electro-optical logic circuits can be formed; and
(3) The number of picture elements can increase by an increase in the number of the cells when the length of time (duty factor) where a voltage is applied to respective picture elements is fixed in driving the panel in a multiplexing manner. Nevertheless, the display panel is difficult to reduce to practice primarily because of deterioration of display quality.